What key feature must be demonstrated in bipolar II disorder?

Bipolar II disorder is characterized by a pattern of depressive episodes and hypomanic episodes, but crucially, it does not involve manic episodes. This distinction is fundamental to the diagnosis of bipolar II disorder.

In bipolar II disorder, the hypomanic episodes are less severe than full-blown manic episodes and may not significantly impair functioning, while the depressive episodes can be quite intense and debilitating. The absence of manic episodes is what differentiates bipolar II from bipolar I disorder, where individuals experience at least one manic episode.

Therefore, the key feature that must be demonstrated in bipolar II disorder is indeed the lack of history of manic episodes, as this is a defining aspect of the disorder and necessary for appropriate diagnosis and treatment.